This invention relates to thin film resistors and in particular to a geometry and method of fabricating such resistors which permit attainment of high resistances.
Thin film resistors have long been important where precise resistance values are needed. A wide range of resistance values is presently available due to the ability to pattern generate and laser trim the resistor. However, present resistors have not generally exceeded 2-3 megohms in resistance. This is due to the fact that higher value resistances generally require either an excessively large pattern or a narrow line width (preferably approximately 12 .mu.m for resistors formed on ceramic) which is more susceptible to faults producing either an open circuit or short circuit in the resistor. A short usually just requires additional trimming to correct, but a single open in the resistor pattern renders the resistor useless after laser trimming.
Thus, attempts to extend the resistance range upward create a greater probability of open circuit faults and result in significant yield problems.
It is, therefore, a primary object of the invention to provide a resistor geometry and method of fabrication which are tolerant of faults in the film, thereby permitting fine line patterns and high resistance values.